An anti-counterfeiting manner involves using steganography to conceal message (regarding the copyright) in the documents and images. For example, U.S. Pat. No. 8,594,453 discloses a conventional method for creating a data-bearing halftone image in the form of a stegatone (steganographic halftone).
As shown in FIG. 1, a cell of a grayscale image may be converted into a stegatone using one of the four stegatone cells 502, 504, 506 and 508. Each of the stegatone cells is associated with a binary code having two bits (e.g., ‘00’, ‘01’, ‘10’ and ‘11’). As such, a message (e.g., a copyright claimer) in the form of a stream of binary codes may be represented by a series of stegatone cells which composes the data-bearing portion of the data-bearing halftone image.
However, the arrangements of the grayscale image using the stegatone cells are deliberately made. As a result, the quality of the generated data-bearing halftone image may be compromised.
Other documents related to the art include:
D. J. Lieberman and Jan P. Allebach, “A dual interpretation for direct binary search and its implications for tone reproduction and texture quality,” IEEE Trans. Image Processing, Vol. 9, Issue 11, pp. 1950-1963, 2000. (doi:10.1109/83.877215);
Xiaotian Wu, Duanhao Ou, Juan Liu, and Wei Sun, “Data hiding in halftone images with homogeneous distribution of embedding positions,” Optical Engineering, Vol. 51, Issue 3, pp. 1-13, 2012. (doi:10.1117/1.OE.51.3.037005); and
Ming Sun Fu and O. C. Au, “Data hiding watermarking for halftone images,” IEEE Trans. Image Processing, Vol. 11, Issue 4, pp. 477-484, 2002. (doi:10.1109/TIP.2002.999680).